CA1154673A - Injectable rabies vaccine composition and method for preparing same - Google Patents

Abstract

ABSTRACT

An injectable rabies vaccine composition is disclosed which comprises a sterilized suspension of a minor concentration by weight of proteineous suckling mice or rat brain par-ticles of injectable particle size laden with inactivated rabies virus in an aqueous buffer solution having a slightly basic pH-value and an amount, dissolved therein, of a buffer composition sufficient to stabilize the pH
at said value, said buffer composition comprising a mixture of an organic base of the formula

Description

6~3 INJECTABLE RABIES VACCINE COMPOSITION AND METHOD FOR PRE-PARING SAME

The present invention relates to an improved rabies vaccine composition and a method for preparing same using viral-laden suckling mice or rat brain tissue.

Rabies vaccines are well known in the prior art and such vaccines are widely used in the treatment of both humans and animals. As is also well known, these vaccines, in order to be completely acceptable and fully effective, must produce or increase immunity to rabies with minimal side effects and the immunity imparted thereby must endure for a reasonably long period of time. Moreover, for these vaccines to be completely acceptable and fully effective, it is necessary that the same be a standardized preparation having a potency which remains relatively constant over reasonably long periods of time. Rabies virus can be grown in a number of tissues and tissue cultures.

In recent years, brains of suckling mice have been used as a suitable source for propagating rabies virus in the preparation of commercial animal vaccines, and the brains of suckling rats have been proposed (see, e.g., Lavender:
Purified Rabies Vaccine (suckling rat brain origin) Appl.

^~5~73 Microbiol. 19, (1970), pp. 923-927). ~enerally, in pre-paring rabies vaccines, a suspension of the viral-laden tissues in a buffered aqueous solution is prepared and then is inactivated. The pH-value of the buffered sus-pension and the inactivated vaccine composition is ad-justed to a slightly basic value. A phosphate saline buffer solution is conventionally used for this purpose.
However, several serious dificulties are encountered in conventional rabies vaccines containing a phosphate buffer:

a) in order to maintain the desired slightly alkaline reaction and the buffering capacity of the phosphate buffPr during the inactivation period, the pH-value of the suspension has to be repeated:Ly adjusted by adding potassium hydroxide solution;

b) the potency of the inactiva~ed vaccine composition relative to the amount of viral-laden tissue is adversely affected by the presence of the phosphate buffer; and c) the pH-value of the vaccine composition is stabi-lized only for a limited period of time after which the pH-value slowly decreases. This change towards an acid reaction causes serious problems in that acidity is detrimental to potency and is a false indication of bacterial contamination of the vaccine. Since contamination of a vaccine with bacteria usually leads to acidification of the vaccine composition, determining the reaction of a vaccine composition with the p~ indicator agent phenol red is used as a simple method for detecting bacterial contamination of vaccine compositions. After a storage period of 9 to 1~ months conventional phosphate buffer containing rabies vaccine compositions often react posi-tive to the phenol red test, even though they are not contaminated at all. Due to this false indication of bacterial contamination large amounts of vaccines are unnecessarily discarded.

The present invention provides a rabies vaccine compo-sition, wherein the drawbacks of the prior art rabies vaccines are avoided or substantially reduced.

In particular, the present invention provides such a vaccine composition wherein the potency relative to the amount of viral laden tissue therein is increased, which is storage-stable and wherein the p~-value is stabilized within a slightly basic range for a prolonged period of time. Also, the vaccine is a standardized preparation and will remain potent over a relatively long period of time. The vaccine will produce or increase immunity to a rabies with minimal side effects, and, when used, will 61J~

provide immunity over a relatively long period of time.

This invention also provides a method for preparing such vaccines, in particular a method wherein no repetitive addition of potassium hydroxide solution is needed for maintaining the pH-value of the composition during the inactivation period.

The rabies vaccine composition of the present invention comprises a sterilized suspension of a minor concentration by weight of proteinous suckling mice or rat brain par-ticles of injectable particle size laden with inactivatedrabies virus, in an aqueous buffer solution having a slightly basic pH-value and an amount, dissolved thereln, of a buffer composition comprising a mixture of an organic base of the formula R~
N C CH OH

2 CH2H

wherein Rl and R2 each are hydrogen or CH2CH20H and an acid addition salt thereof with an acid the anion of which is-compatible with virus replication.

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According to the present invention there is further pro-vided a process for preparing the above defined rabies vaccine composition which comprises the steps of:

(a) suspending asufficient amount of vïral laden suckling mice or rat brain tissue material in a sterilized aqueous buffer solution having a slightly basic pH value and an amount, dissolved therein, of a buffer composition suffi-cient to stabilize the pH at said value, said buffer com-position comprising a mixture of an organic base of the formula where~n Rl and R2 each are hydrogen or CH2CH20H, and an acid addition salt thereof with an acid the anion of which is compatible with virus replication, to obtain a concen-15 ~ trated suspension having suspended therein an amount of ` at least about 20 percent by weight of proteineous viral laden suckling mice or rat brain tissue material;

(b~ comminuting the suspended viral laden suckling mice or rat brain tissue material within the concentrated sus-_ :.

.

- ~c~ .t3~3 ~; _ pension into particles of injectable particle size;

(c) diluting the concentrated suspension with a suffi-cient amout of saidsterilized aqueous buffer solution to obtain a dilute suspension having a concentration of the proteineous viral laden brain particles of no greater than about 10 percent by weight;

(d3 inactivating the dilute suspension; and (e) adjusting the concentration of viral laden brain particles in the inactivated suspension to obtain the vaccine composition.

As used herein MLD50 refers to the dilution at which death loss of 50% of the mice occurs.

The rabies vaccine composition according to the present invention is prepared and used in form of a sterilized suspension of proteineous suckling mice or rat brain particles of injectable particle size laden with the inactivated rabies virus in the aqueous buffer solution having a slightly basic pH-value. In this regard, it should be noted that the proteineous viral laden material will generally be suspended in the aqueous buffer solution such that the same will provide the virus in the final .

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produc~ in a concentration sufficient to provide the desired antigenic response.

The aqueous buffer solution which is used within the vaccine composition according to the present invention contains a buffer composition comprising a mixture of an organic base of the formula:

Rl~
~ f CH OH

? CH2H

wherein Rl and R2 each are hydrogen or CH2CH20H and an acid addition salt thereof with an acid the anion of 1~ which is compatible with virus replication.

~mong the above bases tris(hydroxymethyl)aminomethane is preferred. ~owever, N-(2-hydroxyethyl)amino-tris(hydroxy-methyl)methane and N,N-bis(2-hydroxyethyl)amino-tris(hydroxy-methyl)methane can also be used.

Any organic or inorganic acids which are not detrimental to virus replication are suitable within the acid addition salts. Hydrochlorides are preferred. Other suitable acid salts include salts of inorganic-acids such as carbonates, 6~

nitrates, and salts of organic acids such as acetates, benzoates, maleates, oxalates, and succinates.

Most preferred is a mixture of Tris(hydroxymethyl)amino-methane (~hich in the following will be abbreviated as Tris) and its hydrochloride (which in the following will be abbreviated as Tris-HCl). The ratio between the free base and its salts within the above buffer composition of course will vary depending an the desired pH-value in the vaccine composition and the particular buffer sub-stances which are used.For example, in order to achieve apH-value of between 7.5 and 8.4 at a temperature of about 25C, a by weight ratio of Tris/Tris~HCl of between about 1.18/6.35 and about 4.03/2.6~ is suitable. Both Tris and Tris-HCl are commercially available.

Preferably the vaccine composition is buffered to a pH-valuè of between about 7.8 to 8.0, and most preferably to a pH-value of about 7.8 at a temperature of about 25C. Accordingly, the buffer solution most preferable is an about 0.05 M Tris/Tris HCl buffer solution containing about 5.32 g/l of Tris-HCl and about 1.97 g/l of Tris and having a pH-value of about 7.8 at a temperature of 25C.

The buffer solution can be prepared by dissolving appro-' ' priate amounts of the base and its salt; e.g., of Tris and of Tris-~C1, in deionized water, or by dissolving an appropriate amount of the base, e.g., Tris, in deionized water and forming the salts in situ, by adding such an amount of the respective acid, e.g., a hydrochloric acid solution, to the solution that the pH of the initially basic solution is adjusted to the desired value. Equally the pH of an initially acidic solution can be adjusted to the desired pH-value by addition of a solution of the base.

An indicator dye such as phenol red may be added, when desired, to facilitate the adjustment of the pH and to monitor the pH during storage. Generally, when phenol red is employed the same will be added in a concentra-tion ranginy between about 1 and about 2~ and the same will, generally, be used as a 1% solution thereof.
Following the pH adjustment, the solution will be steri-lized in accordance with methods known in prior art. For example, the same may be sterilized by heating to a temperature between 120 and 121C for a period of tima between about 30 and 60 minutes.

When desired, preservatives, e.g., antibiotics such as penicillin, streptomycin and amphotericin B, may be added ~ 6~;~3 to the buffer solution or to the suspension of proteineous viral laden particles when the same is prepared.

The viral laden brain tissue from suckling mice or rats is mixed with a sufficient amount o~ the buffer solution to form a concentrated suspension, preferabl~ containing between about 30 and about 60 wt% of the vixus laden brain tissue. Suitably, the buffer solution will contain the buffer composition and all antibiotics required to ma~e a final vaccine concentration between about 10 and 30 units of penicillin, 10 and 30 mcg of streptomycin sul-fate and between about 5 and 10 mcg of amphotericin B
per milliliter of final vaccine product. The suspension will then be subjected to high shear agitation so as to reduce the size of the brain particles to a size suit-able for injection. Suitably, the high shear agitationwill be continued until the particle size of all particles is within the range of about 1 to about 10 microns.

The resulting suspension may be stored at a temperature between about -40 and about -60C. All tests required to insure the viru~ containing suspension of satis-factory quality will be completed prior to use of the stored virus containing suspension. Generally, this sus-pension comprising living, fully virulent virus will be .

tested for purity, safety, and potency. When the sus-pension is to be used in the preparation of a vaccine product, it is essential that the suspension exhibit satisfactory purity and safety and that the same have a virus titer of at least 105MLD50 per 0.01 ml at a con-centration of 3 wt% (for a one-year vaccine), and at least 10 MLD50 per 0.01 ml at a COnCentratiQn of 6 wt%
~for a three-year vaccine~.

As has been noted, supra, the brain tissue material which is laden with the living, fully virulent viruses to be used in the vaccines of this invention will, generally, be stored in a frozen state and it will be necessary to thaw the same prior to preparation of the vaccine.
When the virus laden brain tissue material to be used in the vaccine is frozen, the same will yenerally be rapidly thawed and then diluted with the buffer solution to a concentration ranging between about 2 and about 10 wt%.

After the suspension of viral laden brain tissue particles has been diluted, the same may then be filtered to remove particles having a size greater than 10 microns or the same may be first treated so as to inactivate the virus contained therein and subsequently be filtered.

~ 6~J3 After the viral laden brain particles have been suitably suspended in the buffer solution, and the pH thereof ad-justed, the same may be inactivated, directly, or the same may be first formulated into a vaccine and the viruses inactivated at this point. In either case, any of the techniques known in the prior art to be useful for this purpose may be employed. For example, chemical in-activation may be accomplis~ed with compounds such as ~-propiolactone, or formalin or other suitable aldehydes, or the virus may be inactivated with ultraviolet light.
Beta propiolactone inactivation is, however, preferred since this method results in minimal antigenic distortion.

When ~-propiolactone is used to inactivate the virus, an aqueous solution containing between about 5 and about 15 volume percent of unhydrolyzed ~-propiolactone will be prepared by dissolving a pharmaceutical grade o~ un-hydrolyzed ~-propiolactone in either distilled or deionized water. Generally, ~he solution containing the unhydrolyzed ~-propiolactone will be prepared at a tem-perature between about 4 and 5C and the same will beadded to the diluted suspension at or near this tempe-rature such that the composite product contains ~-pro-piolactone in a dilution within the range of about 1:1,000 and 1 10,000. The composite product will then be ~ 3 allowed to warm to room temperature and be su~jected to periodic agitation for a period of time of between about 24 to 30 hours. During this time, the ~-propiolactone will be hydrolyzed and upon complete hydrolysis, the virus will be inactivated~ Either before or after inactivation of the virus a conventional suspension stabilizing agent ma~ be added and if necessary the pH-value may be read-justed to a range of between about 7.8 and 8Ø The vaccine thus prepared will have a storage life of at least 24 months at a temperature between about 4 and 5C. It will, of course, be appreciated that the vaccine should be stored under sterile conditions. It will also be appre-ciated that the vaccine may be stored in single or multiple dose containers and that t:he same will be used in accordance with the techniques wel] known in the art.
Generally, a single dose will range between about 1 and 5 ml.

At this point, it should be noted that the suckling mouse or rat brain tissue cannot effectively be separated from the living, full~ virulent rabies virus propagated therein without reducing the virus titer of the resulting viral suspension to an unsatisfactory level. For this reason, the brain tissue should be retained in the vaccine of the present invention. In this regard, it should be :

~ 3 noted that a series of tests completed on test animals with the vaccine of this invention indicate that there is no reaction whatever to the presence of this tissue in the vaccine. It should also be noted that the rabies vaccine compositions prepared in accordance with the present invention exhibit a potency, as determined in mice, of at least ten times the NI~ minimum standard.
It is believed that this increased potency is the result of the relatively high virus titers obtained when the virus is supplied with a high antigenic mass source such as the viral laden suckling mice or rat brain tissue and the vaccine composition is buffered by means of the buffer composition heretofore described. In this regard, it should be noted that these relatively high potencies will be consistently obtained when care is e~ercised to insure the high titers heretofore described and to insure that the final vaccine contains at least about 2 wt% of the viral laden brain tissue.

In the following a method of obtaining the viral laden suckling mice or rat brain tissue which is used as a starting material for the presently claimed rabies vaccine composition will be described:

It has been found that a high antigenic mass rabies virus .

6~3 can be propagated in suckling mouse brain or rat brain tissue and that standardized vaccine preparations can be prepared with rabies virus propagated in this manner.

Generally, vaccine production quantities of a high anti-genic mass rabies virus can be propagated in suckling mouse or rat brain tissue starting with any of thP strains of rabies virus generally availa~le for this purpose. In this regard, the CVS strain of rabies virus has been found particularly effective for use in the propagation of such a high antigenic mass virus. Such viruses are available from the National Institute of Health, Bet:hesda, Maryland, U.S.A. as well as from other Culture Depositories and the same may be obtained as a lyophilized suspension.

The high antigenic mass rabies vir~us can be propagated starting from a lyophilized suspension of a suitable rabies virus obtained from one of the Culture Depositories.
Generally, the lyophilized suspension, when reconstitut~d, will have a virus titer between about 10 and 107 MLD50 per 0.03 ml. This suspension~will then be intracerebrally inoculated into several suckling ~ice or rats. The actual size of the dose is not, of course, critical so long as each of the mice or rats receive a dose sufficient to induce rabies in the inoculated species. Suitably, suckling ~15~6 d 3 - 16 ~

mice will be injected with a dose having a virus titer between about 100 and 150 Ml,D50.

As will be readily apparent, the intracerebral inoculation of the live rabies virus will produce typical rabies symptoms in the mice or rats and permit the rabies virus to propagate through the brain cell tissues. Generally, the virus will be permitted to incubate for a period between about 4 and 5 days and the virus may be harvested after this period. As will be pointed out more fully, hereinafter, uninoculated control litters from the same source of mice or rats will be observed during and after the incubation period to insure that the animals used for propagation did not suffer from abnormal symptoms.

Af~er the necessary tests have been completed to insure that the inoculated animals did not suffer from other diseases, the propagated rabies virus will be harvested by removing the brain of the inoculated suckling animals.
This can, of course, be accomplished by any suitab~e technique known in the art. For example, inoculated sucXling mlce, after having become moribund will be held at a temperature of between about -40 and -60C after the virus incubation period and prior to harvesting. The frozen mice will, then, be thawed just prior to harvest and the ~ 6~3 rabies virus laden brain tissue removed, generally, at or near room temperature. Following the harvest, the rabies virus laden brain will be suspended in a suitable medium and stored at a temperature between about -40 and ~60C. A portion of the brain tissue buspension will, generally, of course, be withdrawn and tested befoxe the remaining portion thereof is used for any purpose~

Generally, the first batch of harvested viral laden brain tissue will be used as a master seed for all future production of liviny, fully virulent viruses for use in the vaccine of this invention. When this is done, the first batch will be extensively tested to insure that the same is completely satisfactory for its intended purpose. As will be readily appare!nt, when the first batch of harvèsted brain is used exclusively to inoculate suckling animals for the purpose of propagating the virus for subsequent vaccine production, a relatively large source of seed virus will be provided and each batch of vaccine produced therewith will be more uniform since each will be started with the virus from the same source.
This results in a more uniform vaccine product and this method of subsequent propagation lS preferred for this reason. Notwithstanding this, however, a continuing supply of living, fully virulent virus could be provided by using a portion of each batch of viral laden brain tissue to inoculate additional suckling mice or rats with the remaining portion used to produce a vaccine in accordance with this invention. As will be readily apparent, however, propagation in this manner would be unfeasible for indu-strial vaccine production due to the extensive tests that must be completed on each batch of seed virus to insure the high quality product of this invention.

When the first batch of harvested viral laden brain tissue is used as a master seed, the same will, generally, be suspended in a suitable media at a concentration of about 20% fetal bovine serum and the suspension will contain about 1000 units penicillin, 1000 mcg streptomycin sul-fate and 10 mc~ amphotericin B per milliliter thereof.
The particular concentration of fetal bovine in suspension is not, of course, critical and the particular concentration employed can be varied. Moreover~ the concentration of antibiotics in the suspension is also not critical~ It is, however; essential that the master seed have a virus titer ~0 of at least 10 MLD50 per 0.01 ml at a 20% concentration to insure the high potency of the vaccine of the present invention.

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Generally, when the first batch of harvested viral laden brain tissue is to be used as a master seed, the same will be subjected to high shear agitation so as to reduce the particle size of the suspended brain tissue to between about 1 and 10 microns. This can, of course, be most easily accomplished by subjecting the suspension to high shear agitation at a relatively high concentration of at least about 20 wt~ and thereafter diluting the same to the desired concentration for storage. Moreover the master seed will, generally, be stored, thawed and used, as required, for subsequent testing and/or the production of working seed.

After a first batch of viral laden brain tissue has been prepared, all subsequent batches of brain tissue con-taining the living, fully virulent rabies virus will beproduced by inoculating suckling mice or rats with viral laden brain tissue. Generally, this will be accomplished, exclusively, with the first batch of viral laden brain tissue which will be preserved as a master seed. As has been noted, supra, however, this can be accomplished by using a portion of the first or any subsequent batch of viral laden brain tissue therefor. In either case, the viral laden brain tissue will be suspended in a suitable ~5'~ 3 diluent and diluted such that each inoculated suckling animal receives a dose which is sufficient ~or inducing rabies. Suitably a suckling mouse receives a dose having a strength of between about 100 and 500 MLD50. Generally, this will be achieved with a dose of about 0.01 ml, although other size doses could be used.

Broadly, any number of mice or rats could be inoculated and the viral laden brains thereof subsequently pooled to produce a vaccine in accordance with this invention.
Generally, however, the number of inoculated animals will range between about 1,000 and 10,000 and about 50,000 and 500,000 doses of a vaccine product will be produced from each such batch. After the inoculation of each batch of suckling animals, the animals will be observed for typical rabies symptoms and the viral laden brain tissuè
harvested after the animals become moribund. In this regard, it should again be noted that the moribund ani-mals can be stored at a temperature between about -40 and about -60C for a period of time of about two weeks.
The moribund animal will, generally, then be stored and alI ~ests necessary to insure that healthy animals were inoculated will be completed before the viral laden brain tissue is harvested. When these tests are completed, the brains will be harvested in the same manner as indicated ~ 6 previously with respect to the first batch prepared and then suspended in a suitable medium. Following this sus-pension, the viral laden suspension will also be tested so as to insure that the same is suitable for the pre-paration of a vaccine within the scope of this invention.

When the rabies virus is to be harvested directly after the animals have become moribund, this can be accomplished directly by extraction of the brain. When the virus is to be harvested from stored animals, however, it will be `~ 10 necessary to thaw the frozen, moribund animals prior to removing the brain. This will, ~enerally, be accomplished by immersing the frozen animal in a water bath at a temperature between 5 and 1~C. The viral laden brains will then be removed at or near room temperature. Though lS this is not necessarily re~uired, the skin surface of the animals may be treated with tincture of iodine prior to extraction of the brain, and the extraction may ke accomp-lished with a suitably sized hypodermic needle inserted tangentially in the forward aspect of the cranial cavity.

Generally, the hypodermic needle will be attached to a safety-trappe~ vacuum system. Generally, the extracted brains will be cooled to a temperature between about -50 and +5C immediately after removal thereof.

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A~ter the brains have been removed from the inoculated suckling mice or rats the obtained virus laden brain tissue material can be frozen or can directly be used within the process accordiny to the present invention.
For example, it may be directly diluted with the buffer solution to form the above mentioned concentrated sus-pension which again can be frozen and for a period of time be stored in frozen form for example until all tests which are required have been performed as samples of sus-pension.

At this point, it should be noted that the various testsperformed on both the primary seed and subsequent batches of viral laden brain tissue form no part of the present invention and all may be completed in accordance with techniques well known in the prior art. Nonetheless, it should be noted that the batch used as the primary master seed would normally be tested for purity, safety, potency, sterility, and identity while subsequent batches of viral laden brain tissue would be tested only for purity, safety, and potency. Safety, on the other hand, may be determined by intracerebrally inoculating any of several animal species with the inactivated virus and observing the in-oculated species for a period of about 21 days. Identity, on the other hand, may be determined by inoculating guinea ~ 6~3 pigs and or mice intracerebrally and observing the develop-ment of typical rabies symptoms; in cell cultures by fluores-cent antibody microscopy, using specific fluorescein labeled rabies antiserum; and by the virus' ability, when inacti-vated, to protect guinea pigs and/or mice against lethalchallenge of rabies virus. Finally, potency may be deter-mined by inoculating any of several animal species, in accordance with known procedures, with a vaccine containing the inactivated virus and determining the minimum concen-tration or dose required to protect the species thus inocu-lated.

In ~eneral, any strain o~ mice or rats may be used to pro-pagate the rabies virus which is most useful in the present invention. Care should be exercised, however, to remove any animals evidencing disease symptoms from the colony.
Any such animals thus removed should then be autopsied and examined grossly and microscopically for specific disease lesions so as to insure that the animals actually used for the propagation of the rabies vaccine are suit- `
able therefor. In addition, representative litters of suckling animals should be routinely examined for LCM virus.
Moreover, the pooled brain su~pensionsshould be routinely tested for murine leukemia particles and serologic end-point titrations should be run on individual samples to ,. ..

~ 3' determine murine virus antibodies for the following: -:
reovirus type 3 (Hl), pneumonia virus of mice (PVM) (HI), K virus (HI), Theiler's encephalomyelitis (GDVII) ~HI), polyoma ~HI~, Sendai (HI), minute virus of mice (MVM) (HI), mouse advenovirus (CF), mouse hepatitis virus (CF), lymphocytic choriomeningitis virus (LCM) (CF) and ectromelia (vaccine virus HI test). In addition, routine cultures should be obtained from the vital organs of several pro-duction females for the purpose of determining the absence of bacterial pathogena. Generally, all of these tests will be completed in accordance with procedures well known in the prior art and all will be completed on the suckling mice or rats used to prepare the master. seed and the same will be routinely accomplished thereafter.

Notwithstanding the fact that esse.ntially any strain of mice or rats could be used to propagate the rabies virus use~
ful in the vaccinesof this invention, it is preferred that a strain known to be useful for medical purposes be usad and most preferred that a germ-free strain be employed for propagation of the virus. In this regard, it should be noted that a germ-free colony of suitable mice has been develo~edand the same is designated as Strain ICR-MCR ~y the supplier, Mld-Continental Research Animals, IncO of Shawnee, Kansas, U.S.A.

~ ,a6~3 In the following the preparation of a rabies vaccine com-position comprising a sterilized suspension of viral laden proteineous suckling mice brain particles according to a preferred embodiment of the invention will be described:

a~ Preparation of starting viral laden suckling mice brain tissue material.

The rabies virus for vaccine production is propagated by injecting suckling mice intracerebrally at an age between two and five days with a working seed containing living, fully virulent rabies virus, which working seed is pre-pared by diluting a master seed to a virus titer between about 100 to S00 MLD50 per dose. The master seed, in turn, is prepared by inoculating 2 - 5 day old suckling mice from the ~ame source as that used for future propagation with a CVS strain rabies virus and then harvesting the viral laden brain tissue. The master see~ has a virus titer of at least 10 MLD50 per 0.01 ml at a concen-tration of 20 wt%~ (In the definition of the virus titer 107-2 indicates the number of virus particles at the specifled quantity and concentration of the mice brain suspension.) The production virus is then harvested from - the inoculated mice after the development of typical rabies symptoms, when the mice have become moribund (4-5 days) .

and when 2-5~ of the inoculated mice have died. The thus propagated virus will be harvested and used only if there is no evidence of atypical rabies virus propagation and only if the results of all tests noted, heretofore, are satisfactory.

Until it is determined that the virus are satisfactory for harvest, the virus laden mice are stored in plastic containers at a temperature between about -45 and -55C.
After satisfactory results have been obtained and the mice are ready for harvest, the mice are thawed by immer-sing the same in water (in the plastic containers) at a temperature between about 5 and 15C. Once the mice have been thawed, the skin surface thereof is treated with tincture of iodine and the brains withdrawn from the cranial cavity using a 15 gauge hypodermic needle inserted tangentially in the forward aspect of the cr~nial caviky in combination with a vacuum aspirator. After the brains have been harvested, the same are pooled together.

b) Preparation of rabies vaccine.

The pooled viral laden brain material is subsequently sus-pended in a 0.05M solution of Tris-HCl/Tris buffer con-taining a sufficient amount of antibiotics to provide 10 6~3 to 30 units of penicillin, 10 to 30 mcg streptomycin sul-fate and 5 to 10 mcg amphotericin B per milliliter of final vaccine product. In the preferred embodiment, the viral laden mouse brains will be suspended, initially, at a concentration of 30 to ~0 wt% and then subjected to high shear agitation so as to reduce the particle size of the suspended mouse brains to between about 1 and 10 microns.

Between about 2 and 10 ml of-the suspension thus pre-pared are withdrawn and diluted for purposes of further tests. The remaining portion is stored at a temperature between about -45 and -55C and subsequently used ~after satisfactory test results have been obtained) in the preparation of a rabies vaccine.

In the preparation of the rabies vaccine, the concen-trated (30 - 60 wt%) frozen suspension is thawed at a temperature of between 4 and 5~C and diluted to a con-centration of about 2.5 to about 6 wt%. Dilution is effected with an aqueous 0.05M solution of Tris/Tris-HCl buffer and may further contain any additional antibiotics which might be required to provide the desired antibiotics concentration in the final product. The diluted suspension then is filtered under sterile conditions to remo~e par-~iLl~C.-a.673 ticles greater than 10 microns. The pH-value of the re-sulting suspension is between about 7.5 and 8.4.

During the dilution, filtration and adjustment of the pH, the suspension is maintained at a temperature of b~tween 0 and 5C. Following the dilution, filtration and pH ad-justment, the rabies virus then ls inactivated with un-hydrolized B-propiolactone. As has been noted, supra, this can be accomplished with a solution containing be-tween aboutl5~and !15 wt~ of unhydrolized ~-propiolactone.
10 The B-propiolactone solution is suitably added to the 1 diluted suspension with both at a temperature of between ¦
about 4 and-5C. Thereafter the combined mixture will be allowed to become fully hydrolized. Generally, this will be accomplished at room temperature within about 24 to about 30 hours. The suspension should be agitated perio-dically throughout the hydrolyzation period.

To insure standardization of the product, the concentration of suspended tissue in the product must be between àbout 2.5 and 6 wt~. The resultiny product may be packaged or stored under sterile conditions.

6'~3 The following Examples will further illustrate the present invention and demonstrate the effectiveness thereof.

Example 1 A) Preparation of viral laden suckling mice brain tissue starting material for a master seed suspensionO

For preparing a concentrated suspension of living, fully virulent rabies virus three 1.0 ml ampules of a 10 wt%
lyophilized mouse brain suspension were obtained from the Division of Biologic Standards, National Institute of Health, Bethesda, Maryland, containing the CVS rabies virus strain. The ampules were identified by Serial No. CVS-31.
The three ampules were then pooled, reconstituted and diluted with an aqueous 0.05M Tris/Tris HCl buffer solution and the diluted suspension was used to intracerebrally inoculate 132, three day old, suckling mice. The inocu-lation was accomplished with a calibrated, automatic syxinge inserted approximately midway into-the cranial cavity at an adequate depth into one of the cerebral hemispheresand each of the inoculated mice received 0.01 ml of the viral suspension. The inoculated mice developed typical rabies :` ` :
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~:l.'t`~6 symptoms after three days and became moribund in about four days. The moribund, inoculated mice were then stored at a temperature of -50C for about two days. Following this period of storage, the virus laden brain tissue was separated from the inoculated mice by first warming the frozen mice to a temperature of 5C, treating the skin surface of the inoculated mice with a 2% tincture of iodine and then withdrawing the brain by inserting a 15 gauge hypodermic needle tangentially in the forward aspect of the cranial cavity. The hypodermic needle was attached to a safety trapped vacuum system which was closed be-tween the harvest of each individual mouse brain. Twenty-five grams of brain tissue were withdrawn from 120 of the 132 inoculated mice.

The stock breeders used to produce the mice which were inoculated in this and subsequent Examples were from the germ-free strain designated ICR-MCR and available from Mid-Continent Research Animals, Inc., Shawnee, Kansas, U.S.A. These breeders were housed in sterile facilities and used solely for the purpose of producing a gnoto-biotic colony of mice to be used to propagate the rabies virus useful in the vaccines of this invention. In this regaxd, it should be noted that this was accomplished by retaining a portion of the progeny of the first and sub-sequent generations for future breeding of suckling mouse breeders and using the remaining portion of the first and subsequent genera~ions directly for breeding of suckling mice tw be used in the propagation of the rabies virus.

B) Preparation of a sterilized buffer solution-A buffer solution was prepared by mixing 5.32 g/l Tris HCl and 1~97 g/l Tris base in 1000 ml deionized water and 2 ml of a 1~ solution of phenol red. The pH of the solution is then at a value of 7.8. The solution was then steri-lized by autoclaving at 121C for 30 minutes and tested for sterility. The suspension medium was found satis-factory for use in the preparation of vaccines and was stored under sterile conditions.
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C) Preparation of a concentrated primary master seed suspension of viral laden suckliny mice brain tissue:

The tissue, which was obtained as described above in step ~ was suspended in 100 ml of a sterilized, aqueous 0.05M solution of Tris-HCl/Tris buffer which contained a sufficient amount of antibiotics to provide 1,000 units of penicillin per liter, 1,000 mcg per liter of strepto-mycin sulfate and 10 mcg amphotericin B per milliliter ~ 6~'3 of suspensionO The resulting suspension contained 20 wt%
of the virus laden brain tissue and the same was subjected to high shear agitation for a period of six minutes so as to reduce the size of the brain particles to a si~e be-tween about 1 and 10 microns. Twenty-five milliliters of the 20 wt% suspension was then removed for testing and the remainder of the 20 wt% solution was then dispensed in 0~5 ml amounts in 200 ampules and stored at -50C.

The concentrated viral suspension prepared by the method of Step C of this Example was tested for purity, safety, potency, sterility and identity. The virus titer of the suspension was found to be 10 ~SLD50 per 0.01 ml there-of and the suspension was found to be satisfactory for use as a primary master seed.

D) Preparation of a diluted secondary master seed sus-pension of viral laden suckling mice brain tissue:

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A secondary mas~er seed was prepared by diluting 0.~ ml of the primary master seed suspension prepared in Step C

with 399.6 ml of a sterilized 0.05 M aqueous solution of Tris-HCl/Tris buffer. A portion of the secondary master seed was tested for sterility and the remainder dispensed in 3 ml ampules and stored at -50C. The secondary master ~L5~ 3 seed of this Example was found to be satisfactory for use in the preparation of additional rabies virus.

E) Preparation viral laden suc~ling mice brain tissue starting material for a vaccine composition:

3 ml of the secondary master seed obtained in Step D were thawed and diluted with a sterilized 0.05M aqueous solu-tion of Tris-HCl/Tris buffer prepared in the mannex des-cribed in Step B so as to provide a suspension of living, fully virulent rabies virus having a virus titer between 100 and 500 MLD50 per 0.01 ml thereof. 0.01 ml of this suspension was then injected intracerebrally into each of 92, two to four day old, suckling mice produced with the breeders described in Step A. Following these inocu-lations, the suckling mice were re!turned to their cages to incubate the virus. ~fter about three days, the inocu-lated mice developed typical rabies symptoms and all of the inoculated mice became moribund after 4-5 days. The moribund mice were then stored at -50C until tests on uninoculated lltters of mice from the same source were ~0 completed. ~
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~fter these tests were completed and satisfactory results obtained, 75 of the stored, moribund mice were then thawed 6~3 ~ 34 -and the living, ~ully virulent rabies viruses harvested by xemoval of the brain tissue from the mice in the same manner as that set forth in Step A. After separation, the brains from these 75 inoculated mice were pooled to y7 eld 15 grams of brain tissue.

F) Preparation of concentrated suspension of viral laden suckling mice brain tissue for producin~ vaccine compositions:

The viral laden brain tissue obtained in Step E was then suspended in a sterilized, 0.05M solution of Tris~
HCl/Tris buffer further containing, for example, 600 units of penicillin, 600 mcg streptomycin sulfate and 50 mcg amphotericin B per ml thereof. Two different sus~
pensions were prepared containing respectively 30 and 60% by weight of the viral laden mice brain tissue in the buffer solution. The 30% suspension is suitable for preparing a vaccine composition providing a one-year immunization period; and the 60% suspension is suitable for preparing a vaccine composition providing a three-year immunization period.

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The 30 and 60 wt~ suspensionswere subjected to high shear agitation in a homogenizer at a temperature of about ~.~5~

5C so as to reduce the size of the brain tissue to avalue of between about 1 and 10 microns. Two milliliters of each suspension was then removed for testing and the remainder stored at -50C. The suspensions were tested for potency, mycoplasma and sterility. As a result of these tests, the 60 wt% suspension was found to have a virus titer of 107-38MLD50 per 0.01 ml at a concentration of 6 wt% and to be satisfactory for use in the preparation of a three-year rabies vaccine. The 30 wt~ suspension was 10found to have a virus titer of 105-37MLD50 per 0.01 ml at a concentration of 3 wt%, satisfactory for a one-year vaccine.
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G) Preparation of inactivated rabies vaccine compo-sitions:

After satisfactory results were obtained in the quality control tests, the concentrated 30 and 60 wt% viral laden mouse brain suspensions obtained in Step F were thawed .
by warm.ing to a temperature of 4-5C and then diluted to form 3 and 6 wt% suspensions respectively by adding 9 ml of the buffer solution prepared-in Step B to one ml of the concentrated suspension so as to produce 375 ml each.
. The diluted suspensions which are maintained at about

4-5'C throughout were then filtered through a sterile.

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~ 6 Millipore clarifying screen to remove particles having a particle size greater than 10 microns. Subsequently 25 ml of each of the suspensions were withdrawn for subsequent testing. The living, fully virulent viruses contained in the remaining portion of each dilute suspension were in-activated with B-propiolactone. The deactivation was accomplished with a solution containing 10 wt~ of ~-propio-lactone. The ~-propiolactone solution was prepared by adding a medicinal grade of unhydrolyzed ~-propiolactone at a temperature of -20C to deionized water at a temperature of 5~C. After the ~-propiolactone was added to the water, the mixture was agitated briefly to insure the formation of a solution and the same was then used directly in the inactivation of the rabies virus in the diluted suspensions.
In this regard, it should be noted that best results are obtained when the ~-propiolactone solution is added to the dilu~ed suspension within five minutes after prepa-ration thereof. The ~-propiolactone solution was trans-ferred to the diluted suspension with sterile filtered air pressure at a rate of 4.0 ml per liter of diluted sus-pension in an amount providing a 1:2500 dilution of ~-propiolactone in the combined product. The suspension was then allowed to warm to room temperature and the same wa~
agitated periodically for a period of 24 hours.

~ ~5 In order to insure a standardized product, it is essential that the final vaccine product contain at least 2.5 wt%
of the viral laden mouse brain tissue extracted from the suckling mice and used in the preparation of the vaccine for a one-year immunization period and 5 wt% for a three-year immunization period in~dogs and cats.

Each of the one and three year vaccines prepared in this Example yielded 310 ml. The vaccine compositions were packaged in a plurality of single and 10 dose vials. The packaging was, of course, accomplished in sterile con-ditions and the containers employed were of the con-ventional borosilicate type. Each of the single dose bottles contained 1.3 ml of the vaccine and the 10 dose bottles contained 11.4 ml each.

Example 2 The vaccine compositions obtained in Example 1 were tested for inactivation by inoculating 0.03 ml intra-cerebrally into mice, 21 days old. In one series of tests, 10 mice were injected with the vaccine composition as 20 ` prepared. In the second series, 10 mice were injected with a l:10 dilution of the vaccine composi~ion and in a third series of tests, 10 mice were injected with the composition dilution of 1:100. The mice in all three t~

series survived during the entire 21 day observation period thus indicating that the rabies virus in the vaccine had been inactivated.

Example 3 The relative potency or antigenic factor of the vaccine prepared in Step G of Example 1 was determined in accor-dance with the procedure set forth for the Modified National Institue of Health potency test, which pro-cedure is summarized in the World Health Organization "Laboratory Techniques in Rabies" 2nd Edition, 1966. The materials and methods used, and results obtained are as follows~

~ . .
Six 100 ml test samples of a concentrated suspension con-taining 60% of viral laden mice brain particles each were diluted tenfold to obtain a 6% suspension.

Three of the test samples were diluted with a buffer solution according to the present invention which had been prepared by mixing 5.32 g/l of the Tris HCl with 1.97 g/l of the Tris base and 7.2 g/l NaCl. Phenol red was added to the solutions at a concentration of 3 mls/l of a 1% solution.

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The remaining three test samples were diluted with a con-ventional phosphate buffered saline solution comprising 0.01M dibasic potassium phosphate and NaCl t7 g/l).

The six resulting dilute test suspensions were inactivated with ~-propiolactone at a concentration of 1:2500 for a 24-hour period carried out at a room temperature (22-23C).

The pH of the six dilute 6~ mouse brain test suspensions was maintained at a pH-value of 7.8 during the inacti-vation period, by using lN KOH if necessary. Table No. 1 below gives the amount of lN KOH which was needed to maintain the pH of the test suspensions at 7.8.

At the end of the 24-hour inactivation period, samples from each of the six test suspensions were aseptically drawn with a volumetric pipet ànd tested for the pre-sence of live virus using the mouse safety test. Dilutionsof 10 , 10 , and 10 were inoculated into 10 mice for eàch dilution of the six test suspensions and observed for 21 days. No rabies deaths attributable to live virus were observed.

An amount of 20% v/v stabilizer was added to each of the ~% mouse brain test suspensions to obtain six test-vaccine .

~c~ 73 compositions. The stabilizer employed was pharmaceutical grade Carbopol supplied by B.F. Goodrich, and was added at a weight/volume concentration of 3 g/l to provide a final stabilizer content of 0.5 g/l in the vaccine com-positions.

Vaccine compositions 1 - 3 contained the Tris/Tris HCl buffer solution and ~accine compositions 4 - 6 contained the phosphate bu~fer solution.

The completed test vaccine compositions were thoroughly mixed by agitation for 2 hours after the addition of the stabilizer.

Samples of the eompleted test vaccine eompositions were taken for safety and potency testing.

VaccinesNo. 1 through 6 were tested for potency using the NIH potency test after eompletion of the final produet to determine the antigenic value of the six experimental lots.

Vaceinesl and 4 were incubated at 37C for 230 hours and the potency of each lot tested.

~ 73 - 4~. -Vaccines 2 and 5 were incubated 54 days at room tempe-rature (22 - 23C) and the potency of each lot tested.

Vaccines 3 and 6 were held in the cooler at 5C for 59 days and the potency of each lot tested~

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The antigenic values obtained from the NIH potency test after incubation for all samples are listed in Table 2 below.

Table No. l Addition of l N KOH during the 24 hour Inactivation Period l0 Tris buffered suspensions Phosphate buffered suspensions Suspension No. l N KOH Added Suspension No. l N KOH Added (ml) (ml~
l 0 4 16 6;~'3 ~2 -Table No. 2 Antigenic Values of Rabies Vaccine Formulated Tris/Tris-HCl Buffered Saline and Phosphate Buffered Saline.

The potencies of the six vaccines were tested by the NIH
Potency test after incubation for 230 hours at 37C, 54 days at room temperature and 59 days at 5C.

Antigenic Values of the VaccinesBefore and After Incubation at 37C for 230 hours.

Antigenic Value Before Incuba-...... Antigenic Value After Incuba-tion tion Vaccine No. 1 Vaccine No. 1 *EPD50 Test Vaccine 156.3 EPD50 Test Vaccine 130.0 EPD50 Ref~ Vaccine 23.07 EPD50 Ref. Vaccine 22.03 Antigenic Value 6.78 Antiqenic Value 5.90 ].5 Vaccine No. 4 Vaccine No. 4 EPD50 Test Vaccine 208.4 EPD50 Test Vaccine 112.2 EPD50 Ref. Vaccine 23.17 EPD50 Ref. Vaccine 17.42 Antiqenic Value . 4.99 Antigenic Value 2.99 _ , ,, ,,, , . . _ . _ .

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Antigenic Values of Vaccines Incubated At Room TempO(22-23C) for 54 ~ays AV Before Storage AV Afer Storage Vaccine No. 2 Vaccine No. 2 -EPD50 Test Vaccine 146 EPD50 Test Vaccine 176 EPD50 Ref. Vaccine 31 EPD50 Ref. Vaccine 27.6 Antigenic Value 7.26 Antigenic Value 6.4 Vaccine No. 5 Vaccine No. 5 EPD50 Test Vaccine 167 EPD50 Test Vaccine 218 EPD50 Ref. Vaccine 23.3EPD50 Ref. Vaccine 37.1 Antigenic Value 4.7 Antigenic Value 2.7 Antigenic Valuesof Vaccine refri~erated at 5C for 59 Days Vàccine No. 3 Vaccine No. 3 EPD50 Test Vaccine 184.2EPD50 Test Vaccine 228 EPD50 Ref. Vaccine 28.5EPD50 Ref. Vaccine 32-.5 ~ntigenic Value 6.46 Antigenic Value 5.07 Vaccine No. 6 Vaccine No. 6 EPD50 Test Vaccine 133 EPD50 Test Vaccine 163 EPD50 Ref. Vaccine 28.5EPD5~ Ref. Vaccine 32.6 Antigenic Value 4.67 Antigenic Value 3.67 *EPD50 is that dose where 50% of the mice are protected when challenged with live rabies virus.
-- ~4 -The results from the above test suspensions confirmed that the pH of ~he Tris/Tris-HCl buffered suspensions did not fluctuate after the addition of ~-propiolactone as did the mouse brain virus suspensions buffered with the phosphate buffer. (See Table 1.) i, The pH of the Tris/Tris~HCl buffered suspensions was buffered at a pH of 7.~ throughout the inactivation pro-cedures and there was lowering of pH (6.9 - 7.2) of the phosphate buffered lots during the same inactivation period and lt was necessary to add 1 N KOH to raise the pH of the phosphate buffered experimental lots. I

Results of the safety test in mice revealed no rabies deaths attributable to live virus in all groups tested~

The results of the NIH potency show that there were dif-ferences in the antigenic values of the vaccines prepared using Tris/Tris-HCl buffer and the vaccines prepared using phosphate buffer (See Table 2.) As will be readily apparent, the foregoing Examples clearly indicate that the vaccines of this invention are completely acceptable and fully effective for the purpose intended.

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~ 7 As is also readily apparent, the rabies vaccine prepared in accordance with this invention does produce immunity in all tested animal species to this disease.

Claims (17)

The embodiments of the invention in which an exclusive property or privilege is claimed are defines as follows:-

1. A rabies vaccine composition stabilized at a slightly basic pH comprising a sterilized suspension of proteineous suckling mice or rat brain particles of injectable particle size laden with inactivated rabies virus in an aqueous buffer solution, characterized in that said buffer composition comprises a mixture of an organic base of the formula wherein R1 and R2 each are hydrogen of CH2CH2OH, and an acid addition salt thereof with an acid the anion of which is compat-ible with virus replication.

2. A process for preparing the rabies vaccine compo-sition as defined in claim 1, which comprises the steps of (a) suspending a sufficient amount of viral laden suckling mice or rat brain tissue material in a steri-lized aqueous buffer solution having a slightly basic pH
value and an amount, dissolved therein, of a buffer com-position sufficient to stabilize the pH at said value, said buffer composition comprising a mixture of an organic base of the formula wherein R1 and R2 each are hydrogen or CH2CH2OH, and an acid addition salt thereof with an acid the anion of which is compatible with virus replication, to obtain a con-centrated suspension having suspended therein an amount of at least about 20 percent by weight of proteineous viral laden suckling mice or rat brain tissue material;

(b) comminuting the suspended viral laden suckling mice or rat brain tissue material within the concentrated suspension into particles of injectable particle size;

(c) diluting the concentrated suspension with a sufficient amount of said sterilized aqueous buffer solu-tion to obtain a dilute suspension having a concentration of the proteineous viral laden brain particles of no greater than about 10 percent by weight;

(d) inactivating the dilute suspension; and (e) adjusting the concentration of viral laden brain particles in the inactivated suspension to obtain the vaccine composition.

3. The process as defined in claim 2, wherein the amount of viral laden suckling mice or rat brain tissue material in the concentrated suspension in step (a) is from about 30 to about 60 percent by weight.

4. The process as defined in claim 2, wherein step (b) comprises subjecting the brain tissue material within the concentrated solution to high shear agitation.

5. The process as defined in claim 2, wherein the in-activating step (d) comprises combining the dilute sus-pension with an unhydrolyzed beta propiolactone solution in an amount to provide a 1:1,000 to 1:10,000 dilution of beta propiolactone in the combined product, and allowing the beta propiolactone to hydrolize.

6. The process as defined in claim 5, wherein in-activation of the rabies virus is accomplished by main-taining said combined product at room temperature for a period of at least approximately 24 hours.

7. The process as defined in claim 6, wherein said combined product is periodically agitated during said period.

8. The process as claimed in claim 5, wherein said dilution of beta propiolactone is approximately 1:2,500.

9. The process as defined in claim 2, which further comprises the step of adding a preservatively effective amount of an antibiotic to the aqueous buffer solution.

10. The process as defined in claim 9, wherein the antibiotic is selected from the group consisting of penicillin, a streptomycin salt, amphotericin B and mixtures thereof.

11. The process as defined in claim 2, wherein step (e) comprises diluting the suspension to a concentration of brain tissue of from about 2 to about 10 percent by weight.

12. The process as defined in claim 2, wherein said step (c) comprises diluting the suspension to a concen-tration of brain tissue of from about 2.5 to about 6 percent by weight.

13. The process as defined in claim 2, wherein in step (e) the concentration of viral laden brain particles is adjusted to from about 2.5 to about 6 percent by weight.

14. The process as defined in claim 2, wherein in step (e) the concentration of viral laden brain particles is adjusted to from about 2.5 to about 3.5 percent by weight.

15. The process as defined in claim 2, wherein in step (e) the concentration of viral laden brain particles is adjusted to from about 5 to about 6 percent by weight.

16. The process as defined in claim 2, wherein the buffer composition comprises a mixture of tris (hydroxy-methyl)aminomethane and its hydrochloride.

17. The process as defined in claim 16, wherein the aqueous buffer solution is a 0.05M solution of said buffer composition.